1. Field of the Invention
The invention relates to a sliding valve comprising:                a valve body with a wall having a valve opening and a valve seat surrounding the valve opening,        a valve plate that can be moved between an open position in which it frees the valve opening, an intermediate position in which it covers the valve opening but is raised from the valve seat, and a closed position in which it is pressed onto the valve seat,        at least one valve rod that can move in the axial direction and can be moved for closing the valve starting from a first position in which the valve plate assumes its open position, to a second position in which the valve plate assumes its intermediate position, and into a third position in which the valve plate assumes its closed position,        at least one lifting element that is activated by the movement of the valve rod from its second into its third position and acts on the valve plate for moving the valve plate from its intermediate position into its closed position, and        at least one support unit with at least one front support element with respect to the closing direction of the valve rod and at least one rear support element, wherein these support elements interact in the closed position of the valve plate with at least one valve-body-fixed, front support element and at least one valve-body-fixed, rear support element, in order to block a movement of the support unit directed away from the valve opening.        
2.Description Of Related Prior Art
Vacuum valves according to a type of sliding valve or plate valve in which the valve opening is closed by the movement of a valve plate that is pressed onto the valve seat surrounding the valve opening have become known in many different constructions. Here, in order not to expose the seal consisting of an elastic material to shearing stress that is too strong, it is known to perform the closing movement of the valve plate in two steps. In a first section of the closing path that comprises the large part of the extent of the closing path, the valve plate is moved from an open position freeing the valve opening into an intermediate position covering the valve opening but still lifted from the valve seat. In the end section of the closing path, the valve plate is moved from the intermediate position into the closed position in which it is pressed onto the valve seat and seals the valve opening.
For a conventional type of sliding valve, this two-step movement process of the valve plate is caused by mechanical lifting elements that are arranged between a plate-shaped support unit moved by a valve rod and the valve plate. These mechanical lifting elements could involve roll bodies that are guided in wedge-shaped gaps between the valve plate and the plate-shaped support unit, lever mechanisms, or tilting elements between these two plates. To avoid or limit bending of the valve rod in the second movement step, the plate-shaped support unit or a support plate is similarly supported by mechanical elements used for spreading open the valve with the plate-shaped support unit against a wall of the valve housing opposite the valve seat. Such sliding valves are known, for example, from U.S. Pat. No. 4,560,141, DE 3 209 217 C2, DE 3224387 C2, and U.S. Pat. No. 3,185,435.
Plate valves or sliding valves in which, in the first section of the closing movement, the valve plate is shifted in a linear fashion parallel to the plane of the valve seat and is shifted in the end section of the closing movement essentially at a right angle to the valve seat and is pressed onto this valve seat, are also designated as L-valves. In the end section of the closing movement, if the movement is realized at an angle to the direction of movement of the first step and at an angle to the plane of the valve seat, then the designation J-valve is also used.
A sliding valve of the type noted above is known from JP 2001-263505 A. The support unit comprises, at least in one part of the shown embodiments, a plate-shaped section that interacts with the valve plate through the use of lifting elements, as well as a U-shaped section by which the support unit is attached directly to the valve rod. The free leg of the U-shaped section, which points in the closing direction of the valve rod, and the front end of the plate-shaped section form support elements that interact with valve-body-fixed support elements. These valve-body-fixed support elements are attached directly to or constructed integrally with the wall having the valve opening, so that a direct force transmission is achieved without a bypass via other walls of the valve body. The contact force of the valve plate onto the valve seat is reached due to the movement of the valve rod from its second into its third position, wherein the valve plate contacts a stop with its front end. While the contact force is building up, this leads to a relative movement both between the rear and also between the front interacting support elements, wherein particles are also generated undesirably.